This invention relates to an apparatus and method for conveying a web of thin flexible material between two locations while providing stability to the web. The illustrated preferred embodiment of the invention has particular relevance to the conveying of plastic film used to wrap articles, but it will be appreciated that the system may be employed in other operating environments as well.
Both mechanical and pneumatic conveyor systems exist in the prior art for conveying plastic wrap and other plastic webs. Conventional mechanical systems, for example systems using vacuum belts or opposed nip forming belts to convey plastic webs, are difficult to maintain and don't perform adequately. Such arrangements are often complex and are not adapted to handle a broad range of web gauges or weights. It has been found, for example, that mechanical devices often lose efficiency as web gauge is reduced. Web instability, particularly in the form of edge flutter and inadvertent folding over of the material, is often a problem with such prior art devices. Obviously, these failings result in a poor wrap and reduced production rates.
Applicant's co-pending U.S. patent application Ser. No. 06/375,793, filed May 7, 1982, relates to an air conveyor system; however, the invention disclosed in that application is used for serially conveying discrete flexible articles, and is not appropriate to the conveying of continuous webs, the specific area which the present system addresses.
While there are pneumatic web conveyors in existence, as stated above, such systems do not maintain sufficient control over the web to prevent distortion thereof, particularly in the corners and at the edges, to enable such systems to be employed with plastic film. For example, the pneumatic conveyor shown in applicant's U.S. Pat. No. 4,186,860, while operating highly satisfactorily for many types of web material, does not have the capability of transporting plastic webs under sufficient edge control to allow the film to arrive at its destination in undistorted condition.